Secrets and Lies: The True Story of the Iraq War by Dilip Hiro 564pp, Politico's, £9.99

Millions across the world who marched in the hope of preventing the invasion of Iraq were angered by the fact that their opposition was ignored. If they read this book their anger will be redoubled. But the people who will surely feel even more embittered are those who were taken in, having been persuaded by the arguments of President Bush and Prime Minister Blair to support the war.

Dilip Hiro coolly dismantles the political lies, distortions and obfuscations that allowed the United States and Britain to launch an illegal invasion of Iraq. That he does the job so meticulously - even, arguably, in too detailed a fashion on occasion - makes his overall indictment even more powerful than the scatter-gun approach of other war critics, such as Michael Moore.

Hiro brings to the subject a thorough knowledge of the Middle East, having written extensively about the region in several of his previous 26 books. Here is an author for whom, to paraphrase Bush's secretary of defence, Donald Rumsfeld, there are no unknown unknowns. He has made it his business to know exactly how Bush's White House team managed to prosecute a war based on a giant fabrication. That, of course, was the claim that Iraq's dictator, Saddam Hussein, had defied the United Nations by holding on to weapons of mass destruction that presented a threat to global stability. In order to support the central lie, to give it the semblance of credibility, there were scores of intertwined supporting lies. Saddam was not linked to al-Qaida and was not, therefore, responsible for 9/11. He did not buy uranium oxide from Niger. Iraq did not have a fleet of unmanned aircraft nor did it have mobile labs to produce chemical and biological weapons. Nor was it operating poison factories.

Hiro is painstaking as he holds up every piece of fake intelligence to scrutiny, revealing both its falsity and the propaganda use to which it was put. Every excuse advanced by Bush and Blair for the invasion is shown to be hollow, as they seek to conceal the main reason for their pre-emptive strike: the desire for regime change. In some of the most telling passages, Hiro reveals the key roles played by the sinister group who surrounded Bush, such as his deputy, Dick Cheney; Rumsfeld's deputy, Paul Wolfowitz; the under secretary of defence, Douglas Feith; the defence adviser Richard Perle; the president's chief political adviser, Karl Rove; and, of course, the national security adviser, Condoleezza Rice. Meanwhile, the senior man, Colin Powell, the secretary of state, was largely isolated from Bush's gung-ho squad. Despite his policy disagreements however, he performed important tasks on behalf of the warriors, none more so than his lengthy speech to the UN Security Council in the build-up to the invasion. Hiro's point-by-point rebuttal of Powell's allegations is masterly.

In similar fashion he destroys the so-called evidence in Blair's now infamous dossiers on WMD and the far-fetched claim about Iraq being able to deploy such weapons within 45 minutes. Evidently, even the Americans scoffed at the statement, though they grew less concerned themselves about the WMD reasoning because they had successfully convinced their public that Saddam was one of the 9/11 culprits.

Hiro mounts convincing evidence that Bush was determined to invade Iraq on virtually any pretext soon after his first election victory. He also shows how, some seven months before the war, US special forces were operating within Iraq at the behest of Rumsfeld. Their work was specifically linked to an invasion that had not even been raised with the UN and while its weapons inspectors were still carrying out their tasks with what later transpired to be great efficiency.

The geopolitical manoeuvres are certainly riveting, but the more human, and inhuman, story emerges in the passages that tell of the invasion itself. There are several examples of just how badly the civilian Iraqi population suffered as the Anglo-American forces swept through their country. But the haunting moments come, just as they did in the revelations about the reality of the Vietnam war, when one discovers that neither politicians nor military leaders ever tell the truth. For example, the Pentagon strenuously denied that it had used napalm in Iraq, despite an Australian correspondent witnessing its use. That wasn't napalm, said a spokesman, it was a Mark 77 firebomb. As Hiro observes this statement was "cynical sophistry", since the Mark 77 is a mixture of kerosene and polystyrene, while napalm is a mixture of jet fuel and polystyrene. The result is just the same: death in a fireball.

There were also official denials about the use of lethal, and indiscriminate, cluster bombs. Yet Hiro is not only able to state that 1,566 cluster bombs were dropped along with more than 20,000 cluster munitions, he also reproduces a map to show exactly where they were used.

In the greater scheme of things it was a small lie, just one among so many. The promulgation of pre-war lies was followed by further lies during the war. Now Bush and Blair tell us that life in post-Saddam Iraq is improving. But why should we believe them?

&£183; Roy Greenslade is professor of journalism at London's City University. To order Secrets and Lies for £9.99 with free UK p&p call Guardian book service on 0870 836 0875 or go to www.theguardian.com/bookshop